It ended up with order sanity checks being implemented for all manual trading systems at Mizuho. Things like blocking an order if it's more than 10% away from the market mid, etc.
You shouldn't fix an issue like this with UI validation alone - it needs to go between the component that creates orders and the stock exchange, so that it also protects against software bugs. For instance, a possible bug is a developer multiplying the order size by the lot size in the backend, when it has already been multiplied in the frontend, causing huge orders to be sent. Sanity checks can catch this.
Automated trading systems have traditionally been under a lot of scrutiny, and nobody in their right mind would run one without sanity checks and a kill switch. That incident taught Mizuho that manual trading can, in fact, also be quite dangerous :)
You shouldn't fix an issue like this with UI validation alone - it needs to go between the component that creates orders and the stock exchange, so that it also protects against software bugs. For instance, a possible bug is a developer multiplying the order size by the lot size in the backend, when it has already been multiplied in the frontend, causing huge orders to be sent. Sanity checks can catch this.
Automated trading systems have traditionally been under a lot of scrutiny, and nobody in their right mind would run one without sanity checks and a kill switch. That incident taught Mizuho that manual trading can, in fact, also be quite dangerous :)